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New trends and material usage in bicycle frame design
Jelínek, Vladimír ; Němec, Karel (referee) ; Juliš, Martin (advisor)
Thesis in its first part summarizes the evolution of the bicycle from the draisine to the low wheels with a focus on the material of the frame of the bicycle. Also discussed in this section is an overview of small structural modifications, which were gradually used on a bike, like Bowden brake or the first type of transmission system. In the second part, the thesis describes the operating principles and types of suspension forks and disc brakes. Mentioned are materials that are currently used for bike frames with a focus on the advantages and disadvantages of each material used and its future anticipated use.
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Corrosive Degradation of Austenitic Steels
Vykoukalová, Tereza ; Juliš, Martin (referee) ; Klakurková, Lenka (advisor)
The main requirement imposed on stainless steel is a high corrosion resistance in aggressive environment. The main aim of the thesis is a numerous group of corrosion resistance stainless steels, i.e. the stainless steel with austenitic matrix. Increased attention is paid to the corrosive attack and corrosion rate of three chosen materials with austenitic matrix in four different corrosive environments (30% solutions of sulphuric acid, nitric acid, acetin acid and sodium chloride). The method of light microscopy was used to study corrosive degradation of different materials.
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Modern diagnostic methods use in defectoscopy
Vítámvás, Zdeněk ; Stránský, Lubomír (referee) ; Juliš, Martin (advisor)
Nowadays non-destructive testing offers various ways to detection defects in material. By selecting of suitable method or suitable combination of tests we can locate the defect and determine size of defect with sufficient accuracy. For higher probability of detect defects and for easier operation and evaluation are still evolve new ways of inspection. There are summarizes both ordinarily and modern methods using in defectoscopy in this work. There are describe its principles, courses of testing, suitability of use and there are drop next general information.
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Low Cycle Fatigue of Magnesium Alloy AZ91
Julišová, Martina ; Podrábský, Tomáš (referee) ; Juliš, Martin (advisor)
The objective of the present study is to investigate the fatigue characteristics of cast magnesium alloy AZ91 after low–cycle fatigue tests at the indoor temperature. Squeeze casting specimens in both non–thermal treatment cast state and in solution annealing state were used as the experimental materials. Cyclic hardening/softening and fatigue life curves were obtained from the tests varying according to the way of thermal treatment. This bachelor thesis includes also fracture tests of specimens. Light microscopy and scanning electron microscopy were used for the investigation.
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Structure and Properties of Aluminium Cast Alloys
Samek, Petr ; Podrábský, Tomáš (referee) ; Juliš, Martin (advisor)
The bachelor work is focused on favour of relationship between structure and porperties of aluminium cast alloy AlSi7Mg0,6 in dependence of the effect of cooling rate. The AlSi7Mg0.6 alloy is commonly used in foundry industry to produce high stressed automotive components like motor blocks and cylinder heads. The properties of the material correspond directly to their microstructure which is given by the parameters of the solidification process. Within the frame of experiment were got structural characteristics (DAS, porosity) depending up on method of cooling. There were watched location of structure defects in volume of specimens.
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Effect of plasma sprayed AlSi coating on low cycle fatigue properties of cast superalloy Inconel 738LC
Obrtlík, Karel ; Pospíšilová, S. ; Juliš, M. ; Čelko, L. ; Podrábský, T.
Air plasma spraying was applied to obtain AlSi protective surface coating on cylindrical specimens of cast polycrystalline superalloy Inconel 738LC. Chemical composition of the surface treated layer was studied and the hardness depth profile was measured. Surface treated and untreated specimens were cyclically strained under total strain control at 800 °C in air. Cyclic stress-strain response and fatigue life of both materials were obtained. The coating results in a slight decrease of cyclic stress-strain curve. A detrimental effect of the surface treatment on derived Wöhler curve is documented while Manson-Coffin curves of both materials are almost identical. Specimen section observations and fracture surface examinations help to discuss fatigue behaviour of both materials.
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Fatigue behaviour of nickel base superalloy Inconel 738LC at room temperature
Juliš, M. ; Obrtlík, Karel ; Petrenec, Martin ; Podrábský, T.
Total strain controlled tests have been performed on cylindrical specimens of Inconel 738LC polycrystals at room temperature (23 °C). Cyclic hardening, cyclic stress-strain and fatigue life curves were obtained. Fracture surface was studied using scanning electron microscopy. High amplitude cycling results in early pronounced hardening followed by secondary hardening. Low amplitude cycling is characterized by the stable stress response. Manson-Coffin and Basquin laws can reasonably approximate the fatigue life data. Fatigue crack initiation close to the surface from casting defects is documented.
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